dts: Cleanup warnings associated with flash and memory nodes

We get several warnings of the form:

	Warning (unit_address_vs_reg): /flash: node has a reg or ranges
	property, but no unit name

or

	Warning (unit_address_vs_reg): /memory: node has a reg or ranges
	property, but no unit name

Fix by adding unit address that is missing to flash & memory nodes.
Additionally the Silabs memory nodes didn't have a compatiable or
device_type, so add those properties as well.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>